Digital tomosynthesis is an imaging technique that enables three-dimensional (3D) imaging of the patient. Acquisition of tomosynthesis images is performed using a large-area digital detector that is typically used for conventional single projection radiography. 3D data is reconstructed from a number of imaged slices through the anatomy, each slice being parallel to the detector plane.
In conventional tomosynthesis, an X-ray source delivers multiple exposures during a single “sweep” from multiple projection angles. Conventional tomosynthesis acquisition consists of a number of projections of X-ray exposures covering an angular range less than 180 degrees, typically 20 to 50 degrees. The system includes only one X-ray source. The patient stands near the detector plane during the tomosynthesis scan. The number of projections for a single wallstand scan can range from about 30 to 60. The sweep angle is the angle from the first to the final projection focal spot with respect to the focal plane.
The X-ray source is moved to different focal spot positions and a projection image is acquired at each position. After tomosynthesis acquisition, the digital images acquired at the detector are reconstructed into multiple image slices, parallel to the flat panel detector face, using a computerized reconstruction algorithm. The flat panel detector provides rapid response, excellent dynamic range and digital images for input to the reconstruction software.
Viewing reconstructed slices is the customary and primary method of visualizing digital tomosynthesis imaging data. However, a common complication of the process of slice reconstruction is reconstruction artifacts. The artifacts result mainly from an insufficient number of projections, limited angle of data acquisition, and ill-posed nature of the limited view reconstruction.
Motion of a patient also causes complications in visualization of tomosynthesis data as reconstructed slices. Conventional slice reconstruction processes assume an immobile imaged object. However, an imaged patient can and often does move relative to the imaging system. Since these exams take several seconds—heart, vascular and respiratory motion is usually inevitable and will lead to motion artifacts in slices.
In certain applications, measuring the extent of motion can be very important. For example, in radiation therapy applications involving moving organs, adequately distributing radiation dosage to hit the moving target is very important. As another example, in planning a minimally invasive surgery or a surgical biopsy, a fairly accurate knowledge of the organ motion would help plan for accessing the target region.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for reducing artifacts in digital tomosynthesis 3D image. There is also a need for improved measurement of patient motion during the image acquisition.